I haven't played either of the Fallout games, but I really hope that they put this feature into Skyrim. It was probably conceived by Obsidian and not Bethesda though, but a guy can hope.
Anyway, looking at the list of Hardcore mode's tweaks, I would incorporate something about body temperature. You would have to take into account weather, clothing, climate, etc. If you get wet, your clothes are heavier and you lose heat faster. Something like that seems like it could be interesting.
Also, since these tweaks seem to be leaning towards realism, I think it would be fun if combat got more dangerous, and looting (and selling) would be more realistic. Basically, you can loot everything a person had on them, but it will weigh you down and noone is going to realistically pay you for some old, used, bled on clothing.
